The present invention relates to the production of refractory linings or walls and has for an object a method of and apparatus for performing the sintering of refractory linings. The invention is more particularly applicable to the sintering of the linings of vessels utilised in metallurgy to contain, heat or process metals in the liquid state.
Vessels of this kind are formed from mixtures of refractory compounds in the form of compacted puddled clay tamped between the outer shell of the vessel and a metal former retaining the material at the inner side of the lining, or of hollow stacked bricks or else of a refractory coating applied by spraying on to a rigid carrier. These refractory materials are exposed to a sintering treatment which is essential to endow the refractory lining with a particular degree of mechanical strength before the first time it is used. This treatment does not have advantages only however, and the sintering conditions have a substantial bearing on the properties of the linings obtained, in particular on the service life of the walls or linings of metallurgical containers.
Commonly speaking, the refractory materials utilised in the applications of this nature are most frequently metal oxides such as silica, alumina, magnesia, zirconia, requiring sintering temperatures of the order of 1500.degree. to 1700.degree. C. which may as known be generated in homogenous manner in arc furnaces. The heating operation within an arc furnace is not appropriate for applications of this kind, however.
In the case of containers like metallurgical ladles and furnaces, which are intended to contain liquid metal, the prevailing trend is towards in situ sintering.
In the case of induction furnaces, this sintering action is obtained by heating by means of an air-gas burner installed in the container close to the inner surface of the linings, prior to infeed of the metal allowing of heating by induction, which may initially be cold and solid or liquefied beforehand.
In the case of ladles, this fritting action is secured by heating by means of an air-gas burner installed in the container close to the inner surface of the linings. The burners utilised do not however allow temperatures of the order of 1200.degree. C. to be exceeded, and in all cases, it is consequently metal in the liquid state at approximately 1500.degree. C. which is in contact with the refractory linings when the sintering action can begin; this liquid metal also originates from the melting of a non-recoverable mold or former, which melting action sets in before the onset of the sintering action as such. Because of this, it is unavoidable for liquid metal infiltrations to occur through the as yet unsintered pulverulent refractory materials.
These infiltrations certainly represent disadvantages: useless metal losses, power losses, irregular and uncertain course of the "fritting" action within the thickness of the linings, mechanical weak spots and heat bridges across the refractory material, premature attrition of the refractory material, substantial corrosion and even risks of metal leakages reaching the inductor and the cooling water ducts surrounding the containers, risks of perforations, unless a protective pulverulent layer of sufficient thickness is maintained around the sintered area. Since the sintering front forming a delimitation between these two areas progresses every time the vessel is utilised during induction heating of the liquid metal it receives, the infiltrations represent a primary factor in limiting the service life of the linings. This method also has the disadvantage that the former can never be recovered.
A more specific object of the invention is to allow the above-mentioned disadvantages to be prevented or minimised, and, contrary to the known techniques, it is possible to perform the sintering of the container linings in situ, over their inner surface prior to any contact with a liquid metal, in temperature and homogeneity conditions subsequently prevent infiltrations and restrict corrosion.